Compositions, systems, and methods for planarizing or polishing the surface of a substrate, especially for chemical-mechanical polishing (CMP), are well known in the art. Polishing compositions or systems (also known as polishing slurries) typically contain an abrasive material in an aqueous solution and are applied to a surface by contacting the surface with a polishing pad saturated with the polishing composition. When used for polishing substrates comprising metals, the polishing compositions often comprise an oxidizing agent. The purpose of the oxidizing agent is to convert the surface of the metals into a softer, more readily abradable material than the metal itself. Thus, polishing compositions comprising oxidizing agents in conjunction with abrasives generally require less aggressive mechanical abrasion of the substrate, which reduces mechanical damage to the substrate caused by the abrading process. Additionally, the presence of the oxidizing agent frequently increases removal rates for the metals and increases throughput in a production setting.
As a method for isolating elements of a semiconductor device, a great deal of attention is being directed towards a shallow trench isolation (STI) process where a silicon nitride layer is formed on a silicon substrate, shallow trenches are formed via etching or photolithography, and a dielectric layer is deposited to fill the trenches. Due to variation in the depth of trenches, or lines, formed in this manner, it is typically necessary to deposit an excess of dielectric material on top of the substrate to ensure complete filling of all trenches. The excess dielectric material (e.g., an oxide) is then typically removed by a chemical-mechanical planarization process to expose the silicon nitride layer. When the silicon nitride layer is exposed, the largest area of the substrate exposed to the chemical-mechanical polishing system comprises silicon nitride, which must then be polished to achieve a highly planar and uniform surface.
Generally, past practice has been to emphasize selectivity for oxide polishing in preference to silicon nitride polishing. Thus, the silicon nitride layer has served as a stopping layer during the chemical-mechanical planarization process, as the overall polishing rate has decreased upon exposure of the silicon nitride layer. For example, U.S. Pat. No. 6,544,892 and references cited therein describe polishing compositions which provide selectivity of silicon dioxide to silicon nitride. Also U.S. Pat. No. 6,376,381 describes the use of certain nonionic surfactants to increase the polishing selectivity between silicon oxide and silicon nitride layers.
Recently, selectivity for polysilicon polishing in preference to silicon oxide and/or silicon nitride polishing has also been emphasized. For example, U.S. Pat. No. 6,533,832 describes a purported increase in polishing selectivity of polysilicon to interlayer dielectric materials (e.g., silicon dioxide) through the use of an alcoholamine selected from dialkylethanol amine, alkyl diethanol amine, and 2-dimethylamino-2-methyl-1-propanol.
Despite these polishing compositions and methods, there remains a need in the art for polishing compositions and methods that can provide controlled selectivity of polysilicon relative to silicon oxide and/or silicon nitride. The invention provides such compositions and methods. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.